LEAF(sys_syscall)
lw t0, PT_R29(sp) # user sp
sltu v0, a0, __NR_Linux + __NR_Linux_syscalls + 1
beqz v0, enosys
sll v0, a0, 2
la v1, sys_syscall
lw t2, sys_call_table(v0) # function pointer
lbu t4, sys_narg_table(a0) # number of arguments
li v0, -EINVAL
beq t2, v1, out # do not recurse
beqz t2, enosys # null function pointer?
andi v0, t0, 0x3 # unaligned stack pointer?
bnez v0, sigsegv
addu v0, t0, 16 # v0 = usp + 16
addu t1, v0, 12 # 3 32-bit arguments
lw v1, THREAD_CURDS($2
or v0, v0, t1
and v1, v1, v0
bltz v1, efault
move a0, a1 # shift argument registers
move a1, a2
move a2, a3
1: lw a3, 16(t0)
2: lw t3, 20(t0)
3: lw t4, 24(t0)
.section __ex_table, "a"
.word 1b, efault
.word 2b, efault
.word 3b, efault
.previous
sw t3, 16(sp) # put into new stackframe
sw t4, 20(sp)
bnez t4, 1f # zero arguments?
addu a0, sp, 32 # then pass sp in a0
1:
sw t3, 16(sp)
sw v1, 20(sp)
jr t2
/* Unreached */
enosys: li v0, -ENOSYS
b out
sigsegv:
li a0, _SIGSEGV
move a1, $28
jal force_sig
/* Fall through */
efault: li v0, -EFAULT
out: jr ra
END(sys_syscall)
这里的汇编指令
.section __ex_table, "a"
.word 1b, efault
.word 2b, efault
.word 3b, efault
.previous
是在做什么呢? |